The present invention relates to a method for production of glass and in particular to a method according to which a uniform glass of a large size can be efficiently produced by a sol-gel method without using complicated operations.
For the production of glass, there is a sol-gel method which uses a metal alkoxide. It has been considered difficult to produce a glass of a large size bY this sol-gel method. This is because according to the sol-gel method, fracture often occurs in a dry gel obtained by drying treatment after gelation.
On the other hand, Japanese Patent Kokai [Laid-Open) No. Sho 60-131833 discloses a sol-gel method for producing a glass of a large size which has never been produced by the conventional sol-gel method. However, as is seen from Examples mentioned in the specification thereof, according to this method, and acid such as hydrochloric acid is added to a metal alkoxide such as silicon ethoxide and the mixture is vigorously stirred, then ultrafine silica is added thereto with stirring end then is subjected to ultrasonic vibration, thereafter the resulting clusters are removed by centrifugation, then pH is adjusted with a basic catalyst, followed by gelation, drying and sintering. Thus, not only the steps are complicated, but also the clusters are still present even after ultrasonic treatment and this must be removed by centrifugation.
According to the method disclosed in the above Japanese Patent Kokai (Laid-Open) No. Sho 60-131833, a glass of a relatively large size can be produced by a sol-gel method, but it suffers from the problems of very complicated steps such as addition of ultrafine silica, ultrasonic vibration treatment and centrifugal treatment.
Under the circumstances, the inventor has disclosed in Japanese Patent Application No. Sho 63-32635 that it is possible to efficiently produce a glass of a large size without using complicated operation by a glass producing method characterized in that a sol solution obtained by hydrolyzing a metal alkoxide in the presence of an organic solvent and ammonia water is concentrated until its volume reaches 1.00-1.95 times the volume of the charged metal alkoxide and then the concentrated sol solution is gelled with addition of an aqueous solution of an acid catalyst, then dried and thereafter sintered by heating to obtain the desired glass.
However, the above method of Japanese Patent Application No. Sho 63-32635 suffers from the problems that it is difficult to uniformlY dispersing the acid catalyst in the sol solution, when the aqueous solution of the acid catalyst is added to the concentrated sol solution, because of poor affinity between the sol solution and the aqueous solution of the acid catalyst, and thus sOlids of about 1 mm in diameter are produced in the sol solution to which the aqueous solution of the acid catalyst has been added and bubbles or holes of about 0.5 mm in diameter are apt to be formed in the bottom portion of the finally obtained glass.